Revert 258410 "Only restart ui if we're logged in."

Revert 258410 "Only restart ui if we're logged in."

> Only restart ui if we're logged in.
>
> * Switch to using cryptohome --action=is_mounted instead of manually checking file mounts.
> * oobe_exists can throw an exception as we log in, so handle this.
> * Use the same mechanism for determining if guest is logged in.
> * Move CryptohomePath and the mount-based IsCryptohomeMounted to CrOSTest.
> * Fixup CrOSTest for guest mode.
>
> BUG=
> TEST=manual
> NOTRY=True
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=257996
>
> Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=258135
>
> Review URL: https://codereview.chromium.org/203973003

TBR=achuith@chromium.org

Review URL: https://codereview.chromium.org/207363002

git-svn-id: svn://svn.chromium.org/chrome/trunk/src@258459 0039d316-1c4b-4281-b951-d872f2087c98